U.S. patent number 8,387,220 [Application Number 12/756,071] was granted by the patent office on 2013-03-05 for method of manufacturing a piezoelectric element.
This patent grant is currently assigned to Canon Kabushiki Kaisha. The grantee listed for this patent is Katsumi Aoki, Junri Ishikura, Yasuyuki Saito, Naoari Shibata. Invention is credited to Katsumi Aoki, Junri Ishikura, Yasuyuki Saito, Naoari Shibata.
United States Patent |
8,387,220 |
Ishikura , et al. |
March 5, 2013 |
Method of manufacturing a piezoelectric element
Abstract
Providing a manufacturing method of a piezoelectric element
which contains at least a substrate, a piezoelectric film and an
electrode provided between the substrate and the piezoelectric
film. The method includes providing an electrode on a substrate,
and baking a piezoelectric film after forming the piezoelectric
film on the electrode. The electrode includes a mixture layer
having an electroconductive oxide and a metal mixed therein. The
concentration of the electroconductive oxide in the substrate side
of the mixture layer is higher than that in the piezoelectric film
side of the mixture layer, and the concentration of the metal in
the piezoelectric film side of the mixture layer is higher than
that in the substrate side of the mixture layer.
Inventors: |
Ishikura; Junri (Tokyo,
JP), Shibata; Naoari (Kawaguchi, JP), Aoki;
Katsumi (Yokohama, JP), Saito; Yasuyuki
(Yokohama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ishikura; Junri
Shibata; Naoari
Aoki; Katsumi
Saito; Yasuyuki |
Tokyo
Kawaguchi
Yokohama
Yokohama |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
38557790 |
Appl.
No.: |
12/756,071 |
Filed: |
April 7, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100192341 A1 |
Aug 5, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11723224 |
Mar 19, 2007 |
7732997 |
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Foreign Application Priority Data
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Apr 3, 2006 [JP] |
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2006-101451 |
Mar 2, 2007 [JP] |
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2007-052325 |
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Current U.S.
Class: |
29/25.35; 29/846;
204/192.1 |
Current CPC
Class: |
B41J
2/1632 (20130101); B41J 2/1642 (20130101); B41J
2/1646 (20130101); H01L 41/316 (20130101); B41J
2/1628 (20130101); B41J 2/161 (20130101); H01L
41/0478 (20130101); B41J 2/1629 (20130101); H01L
41/0973 (20130101); Y10T 29/42 (20150115); Y10T
29/49155 (20150115) |
Current International
Class: |
H04R
17/10 (20060101) |
Field of
Search: |
;29/25.35,846,831
;204/192.1 ;310/363-365 ;438/24,25 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1636729 |
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Jul 2005 |
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CN |
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02007479 |
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Jan 1990 |
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JP |
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8-274573 |
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Oct 1996 |
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JP |
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2000-328223 |
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Nov 2000 |
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JP |
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2001-152360 |
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Jun 2001 |
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JP |
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2002-16229 |
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Jan 2002 |
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JP |
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Primary Examiner: Tugbang; A. Dexter
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
This application is a divisional of application Ser. No.
11/723,224, filed Mar. 19, 2007, the contents of which are
incorporated herein by reference.
Claims
What is claimed is:
1. A manufacturing method of a piezoelectric element which
comprises at least a substrate, a piezoelectric film and an
electrode provided between the substrate and the piezoelectric
film, comprising: providing an electrode, which includes a mixture
layer having an electroconductive oxide and metal mixed in the
mixture layer, on a substrate, and baking a piezoelectric film
after forming the piezoelectric film on the electrode, wherein the
concentration of the electroconductive oxide in the substrate side
of the mixture layer is higher than that in the piezoelectric film
side of the mixture layer, and the concentration of the metal in
the piezoelectric film side of the mixture layer is higher than
that in the substrate side of the mixture layer.
2. The manufacturing method of a piezoelectric element according to
claim 1, wherein the electrode is provided on the substrate by
providing an electroconductive oxide layer, the mixture layer
situated on the electroconductive oxide layer and an
electroconductive metal layer situated on the mixture layer on the
substrate.
3. The manufacturing method of a piezoelectric element according to
claim 2, wherein the mixture layer is formed by forcing a plurality
of targets to discharge concurrently by a sputter method.
4. The manufacturing method of a piezoelectric element according to
claim 1, wherein the piezoelectric film is formed by anyone of a
gas deposition method, a sputter method, a sol-gel method or a CVD
method.
5. The manufacturing method of a piezoelectric element according to
claim 1, further comprising providing an electroconductive oxide
layer, wherein the electroconductive oxide in the electroconductive
oxide layer and the electroconductive oxide in the mixture layer
are identical.
6. The manufacturing method of a piezoelectric element according to
claim 5, wherein the electroconductive oxide is an ABO.sub.3
perovskite-type oxide.
7. The manufacturing method of a piezoelectric element according to
claim 5, wherein the electroconductive oxide is at least one
selected from the group including LaNiO.sub.3, LaCrO.sub.3,
SrRuO.sub.3, CaRuO.sub.3, La.sub.1-xSr.sub.xCoO.sub.3, BaPbO.sub.3,
La.sub.1-xSr.sub.xCa.sub.xRuO.sub.3, La.sub.1-xSr.sub.xTiO.sub.3
and SrIrO.sub.3, and compounds thereof.
8. The manufacturing method of a piezoelectric element according to
claim 7, wherein the metal is a Pt group metal.
9. The manufacturing method of a piezoelectric element according to
claim 1, wherein the electroconductive oxide is SrRuO.sub.3, and
the metal is Pt.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element and a
manufacturing method thereof, further to an electronic device and
an ink jet device including the relevant piezoelectric element.
2. Description of the Related Art
A piezoelectric element exhibits the piezoelectric effect, which
produces an electric field due to a strain, and the inverse
piezoelectric effect, which produces a strain due to an applied
electric field. A piezoelectric element which is mainly formed of
lead zirconate titanate (hereinafter, called "PZT") with addition
of an extremely small amount of an element such as represented by
strontium, barium or niobium is used as a piezoelectric film.
Conventionally, production of a piezoelectric element has included:
mixing a raw material powder for a piezoelectric film, pressurizing
the raw material powder to sinter it, machining the sintered
material to form a piezoelectric film, and subsequently holding the
piezoelectric film between electrode materials to polarize the
piezoelectric film, thereby producing piezoelectricity. However,
recently, as a device becomes miniaturized, it becomes necessary to
mount a piezoelectric element on a thinner, smaller area. A
piezoelectric element of an oxide-based substance represented by
PZT is a brittle material, and therefore it has a machining limit
to be thinned up to about 0.1 mm, so that it can be made thin only
up to about 0.1 mm. Further, an effect exerted by an adhesive is
not negligible in a high frequency band. Therefore, in order to
produce a thinner piezoelectric element without a bonding process,
various film formation methods such as a sputter method, a CVD
method, an aerosol deposition method, a hydrothermal synthesis
method and a sol-gel method, etc. have been devised and a
piezoelectric element has been manufactured by way of trial using
such a method.
Particularly, the aerosol deposition method has a high rate of film
formation and recently, particularly attracts attention as a film
formation method. FIG. 1 illustrates a rough outline of an aerosol
deposition device. This method is that, first, gas 6 such as air,
etc. is supplied into an aerosol formation chamber 1 having
material particles such as PZT, etc. put therein, and the material
particles are aerosolized. Then, the aerosolized particles are
directed to a film formation chamber (film forming chamber) 2
connected by a carrier pipe 3, by a differential pressure between
both chambers, the material particles are squirted from a nozzle 4
provided on a front edge of the carrier pipe 3 to a substrate 8 on
a stage 5, forming a film on the substrate 8, and an air within the
film forming chamber is exhausted by vacuum pump 7.
In addition, there is an ink jet device as one of electronic
devices using a piezoelectric element. The piezoelectric element
may be used for an ink jet head of the ink jet device. In the ink
jet device using the piezoelectric element, a system is known that
a pressure is generated by applying a voltage to a pressure
generator using the piezoelectric element to discharge ink. The ink
jet device of this system includes a pressure generator having
laminated layers of a pressure generation member of PZT (lead
zirconate titanate) etc., a metal plate and ceramics, ink as a
flying medium and a nozzle plate having a ink discharge hole. In
the ink jet device having such a pressure generator, heads of
various types such as a type using a bending mode called "Kyzer
type", a direct pressing type called "piston type" and a type using
a shear mode in which a side wall is moved are manufactured in the
market.
When a thin film piezoelectric element is formed, there is a method
by which, first, a lower electrode is formed on a substrate and
next a piezoelectric film is formed by various film formation
methods. Subsequently, processes such as a baking process, a
formation process of an upper electrode and a polarization process
are carried out. To provide a sufficient piezoelectric performance,
a baking process at several hundred degrees Celsius is necessary
after film formation of the piezoelectric film. This baking process
can facilitate enlargement of a crystal grain size and improvement
of crystallization, providing a higher piezoelectric performance.
In addition, the higher the baking temperature is, the higher
piezoelectric performance tends to develop.
However, baking may present a problem that mutual diffusion among a
substrate, an electrode and a piezoelectric film occurs.
Specifically, as described in Japanese Patent Application Laid-Open
No. H08-274573, when a Si wafer is used as a substrate, Ti and Pt
are used as an electrode, and a piezoelectric film is formed of
PZT, then Si, Ti and Pt diffuse into the PZT film and Pb diffuses
into the Si wafer, though there is difference in the degree of
diffusion depending on a baking temperature. As described above, if
diffusion occurs, a Pt component drops out of the PZT film and
further impurities get into the PZT, which presents a problem that
electric characteristics may not be enhanced sufficiently. Also,
when Pb diffuses into the Si wafer, the Si wafer gets hardened,
causing a problem that accurate machining may not be allowed when
the machining is required in a post-process after film formation.
Particularly, when an ink jet head is formed, the backside of a Si
wafer on which a piezoelectric film is formed is often cut to form
a flow path, and at this time, machining is difficult due to
diffusion of the Pb component into the Si wafer.
Moreover, diffusion of a material for a lower electrode into PZT
progresses, a part of the material reaches the upper portion of the
PZT film, and then the PZT film may not often function as a
piezoelectric element because of contacting electrically with an
upper electrode formed after baking. As a film thickness of the PZT
film becomes thinner, this tendency appears more prominently.
Further, there is a problem that a higher baking temperature
oxidizes an electrode itself to provide resistance, so that the
electrode may not work as an electrode. For example, to provide
adherence between a substrate and Pt, use of Ta, etc. as an
adhesion layer has an effect of adherence (see Japanese Patent
Application Laid-Open No. 2001-152360), but tantalum oxide may be
created even at a comparatively low temperature of about
600.degree. C. Also, it is proposed that an electroconductive oxide
film represented by SrRuO3 be used as an electrode (see Japanese
Patent Application Laid-Open No. 2000-328223 and Japanese Patent
Application Laid-Open No. 2002-016229), but specific resistance
starts to increase at about 700.degree. C., then, beyond
800.degree. C., the electrode becomes approximately similar to an
insulating film, so not preferable for an electrode.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a manufacturing
method of a piezoelectric element by which, even if an electrode
and a piezoelectric film laminated on a substrate are baked
together at a high temperature, the electrode is not oxidized and
mutual diffusion among the substrate, the electrode and the
piezoelectric film is suppressed. Further, another object is to
provide an electronic device and an ink jet device having a
piezoelectric element which secures high adherence between each of
layers and further has a better piezoelectric performance owing to
the relevant method.
A first embodiment of the present invention is a piezoelectric
element which includes at least a substrate, a piezoelectric film
and an electrode disposed between the substrate and the
piezoelectric film, wherein the electrode includes an
electroconductive oxide and electroconductive metal, and, on the
substrate side in the electrode, the electroconductive oxide is
contained more than the electroconductive metal, and further, on
the piezoelectric film side in the electrode, the electroconductive
oxide is contained less than the electroconductive metal. Further,
in this embodiment, the electrode above includes an
electroconductive oxide layer situated on the substrate side, an
electroconductive metal layer including electroconductive metal
situated on the piezoelectric film side, and a mixture layer
provided between the electroconductive oxide layer and the
electroconductive metal layer and formed by mixing the
electroconductive oxide and the electroconductive metal.
Moreover, a second embodiment of the present invention is a
manufacturing method of a piezoelectric element which includes at
least a substrate, a piezoelectric film and an electrode disposed
between the substrate and the piezoelectric film, wherein the
method includes providing an electrode on a substrate and baking a
piezoelectric film after forming the piezoelectric film on the
electrode, wherein the electrode is adapted so that, on the
substrate side, the electroconductive oxide is contained more than
the electroconductive metal and, on the piezoelectric film side in
the electrode, the electroconductive oxide is contained less than
the electroconductive metal. Further, in this embodiment, the
electrode above is formed on the substrate by providing, on the
substrate, an electroconductive oxide layer, a mixture layer formed
by mixing an electroconductive oxide and electroconductive metal
situated on the electroconductive oxide layer, and an
electroconductive metal layer situated on the mixture layer.
Further, the present invention provides an electronic device and an
ink jet device using the piezoelectric element of the present
invention above.
According to the present invention, an electrode configuration
between a substrate and a piezoelectric film is adapted as a
laminated configuration including an electroconductive oxide layer,
a mixture layer of an electroconductive oxide and electroconductive
metal, and an electroconductive metal layer, so that high adherence
in each of interfaces between the substrate and the electrode and
between the electrode and the piezoelectric film can be provided.
Further, mutual diffusion of elements between each of layers can be
suppressed at the time of baking of the piezoelectric film. As the
result, baking at a higher temperature can be practiced, providing
a piezoelectric element of which electric characteristics for a
piezoelectric film is sufficiently brought out. Further features of
the present invention will become apparent from the following
description of exemplary embodiments (with reference to the
attached drawings).
Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference
to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a rough outline of an aerosol deposition device
used in a manufacturing method of the present invention.
FIG. 2 is a schematic depiction illustrating the inside of a
chamber of a sputter device used in an example of the present
invention.
FIG. 3 is a schematic depiction illustrating a section of a sample
used for tape peel test carried out in an example of the present
invention.
FIGS. 4A, 4B, 4C and 4D illustrate manufacturing processes of a
piezoelectric element in an example of the present invention.
FIGS. 5A, 5B, 5C and 5D illustrate manufacturing processes of a
piezoelectric element in an example of the present invention.
DESCRIPTION OF THE EMBODIMENTS
A piezoelectric element of the present invention is such that an
electrode provided between a substrate and a piezoelectric film is
adapted as a laminated layer body including an electroconductive
oxide layer (first layer), a mixture layer (second layer) having an
electroconductive oxide and electroconductive metal (metal) and an
electroconductive metal layer (third layer). Then, the
piezoelectric element may be preferably adapted so that the
electroconductive oxide is a main component on the substrate side
(the electroconductive oxide layer side) of the mixture layer
(second layer), the metal is a main component on the piezoelectric
film side (the electroconductive metal layer side) of the mixture
layer (second layer), and concentration of the electroconductive
oxide becomes lower as getting near to the piezoelectric film side
from the substrate side of the electrode (concentration of the
metal becomes lower as getting near to the substrate side from the
piezoelectric film side).
In addition, in the present invention, a boundary between the first
layer, the second layer and the third layer may be defined
indistinctly. That is, for example, the electrode may include one
layer without a distinctly defined boundary and it has
concentration gradients (slopes) of the electroconductive oxide and
the metal along the thickness direction thereof.
A specific example of this configuration, for example, may be
preferably such that an electrode includes at least an
electroconductive oxide and metal, the electroconductive oxide is a
main component on the substrate side of the electrode, and the
metal is a main component on the piezoelectric film side of the
electrode, and further concentration of the electroconductive oxide
becomes lower as getting near to the piezoelectric film side from
the substrate side of the electrode (concentration of the metal
becomes lower as getting near to the substrate side from the
piezoelectric film side). This configuration may be more preferably
such that the electrode includes only the electroconductive oxide
on the substrate side of the electrode and only the metal on the
piezoelectric film side of the electrode. An embodiment will be
mainly described hereinafter in which an electrode includes a
laminated layer body including an electroconductive oxide layer, a
mixture layer having an electroconductive oxide and
electroconductive metal (metal), and an electroconductive metal
layer (metal layer), but, as described above, an electrode
configuration according to present invention is not limited to this
embodiment. That is, a case where a boundary between each of layers
constituting an electrode may not be defined substantially, or an
electrodes includes one layer having a concentration gradient
described above may fall within the present invention.
In the present invention, glass, a Si wafer, a Si wafer having an
oxidized substance layer such as SiO.sub.2 on its surface and the
like may be preferably used as a substrate. The substrate
particularly preferably includes silicon oxide on its surface. The
Si wafer above, also, may include silicon oxide on its surface due
to natural oxidation or positive oxidation.
As an electroconductive oxide used for the present invention, at
least one type selected from the group including LaNiO.sub.3,
LaCrO.sub.3, SrRuO.sub.3, CaRuO.sub.3, La.sub.1-xSr.sub.xCoO.sub.3,
BaPbO.sub.3, La.sub.1-xSr.sub.xCa.sub.xRuO.sub.3,
La.sub.1-xSr.sub.xTiO.sub.3 and SrIrO.sub.3 especially shown by the
ABO.sub.3 perovskite type, and compounds thereof may be preferably
used. These materials may have better adherence to a substrate
having an oxidized substance such as silicon oxide (usually,
SiO.sub.2) on the surface thereof. Further, these electroconductive
oxides have an effect to suppress diffusion of elements due to
baking. A thickness of those electroconductive oxide layers may be
preferably not smaller than 0.1 .mu.m and not larger than 10 .mu.m
to achieve the effect of diffusion suppression described above.
In addition, Pt-group (Ru, Rh, Pd, Os, Ir, and Pt) may be
preferably used as electroconductive metal (metal) because of
better adherence to a piezoelectric film of PZT, etc. Moreover, the
Pt-group scarcely oxidizes or gets insulated even at the time of
baking at about 900.degree. C. Pt may be more preferably used. A
practical thickness of those electroconductive metal layers may be
preferably not smaller than 0.1 .mu.m and not larger than 10
.mu.m.
In the present invention, between the electroconductive oxide layer
(first layer) and the electroconductive metal layer (third layer)
above, the mixture layer (second layer) including the same
electroconductive oxide as that constituting the first layer and
the same metal as that constituting the third layer are provided.
According to this configuration, adherence between the
electroconductive oxide layer and the electroconductive metal layer
can be enhanced. Particularly, the mixture layer is adapted as a
gradient structure (graded layer) in which composition thereof is
changed in the film thickness direction (the direction in which the
first layer and the third layer are opposing to each other), which
can further enhance the adherence between the first layer and the
third layer described above. Specifically, in the mixture layer
(second layer), concentration of the electroconductive oxide is
made highest in an interface with the electroconductive oxide layer
and is gradually reduced toward an interface with the
electroconductive metal layer. A film thickness of such a mixture
layer may be made not smaller than 10 nm and not larger than 1
.mu.m, suppressing peel and providing strong adherence.
For a forming method of the mixture layer above, a method may be
preferably used by which a plurality of targets is forced to
discharge concurrently by a sputter method.
In the present invention, particularly, a PZT-based oxide or a
relaxor-based dielectric material may be quoted for the
piezoelectric film provided on the electrode above. Among them, in
the case of the PZT-based oxide, an oxide indicated by Pb
(Zr.sub.y, Ti.sub.1-y) O.sub.3, where y is in the range of 0.2 to
0.8, may be preferable. Further, in the case of the relaxor-based
dielectric material, at least one type selected from the group
including Pb (Mn, Nb) O.sub.3--PbTiO.sub.3, Pb (Zn, Nb)
O.sub.3--PbTiO.sub.3, Pb (Sc, Ta) O.sub.3--PbTiO.sub.3, Pb (In, Nb)
O.sub.3--PbTiO.sub.3, Pb (Yb, Nb) O.sub.3--PbTiO.sub.3, Pb (Ni, Nb)
O.sub.3--PbTiO.sub.3, and compounds thereof may be suitable.
A practical thickness of the piezoelectric film above may be
preferably not smaller than 1 .mu.m and not larger than 200
.mu.m.
In addition, for a film formation method of the piezoelectric film
above, a gas deposition method, a sputter method, a sol-gel method
and a CVD method etc. may be preferably used.
The piezoelectric element of the present invention may be formed
for providing a piezoelectric film having excellent electric
characteristics, by forming an electroconductive oxide layer, a
mixture layer and an electroconductive metal layer as an electrode
on a substrate, subsequently forming a piezoelectric film, then
applying a baking process. Usually, the electrode above may be a
lower electrode, and further an upper electrode is formed on the
piezoelectric film above, providing a piezoelectric element.
EXAMPLE
A Si wafer was used as a substrate 8 and a lower electrode was
formed as follows.
First, a SrRuO.sub.3 film was formed with a thickness of 300 nm on
the substrate 8 by a magnetron sputter method. Next, a mixture
layer having SrRuO.sub.3 and Pt was formed with a thickness of
about 300 nm. Further, a Pt layer was formed with a thickness of
300 nm. The mixture layer was adapted to have a graded composition
structure in which a ratio of Pt was increased gradually from the
SrRuO.sub.3 layer to the Pt layer. The gradient layer (mixture
layer), as shown in FIG. 2, was adapted in a manner that two
targets 9, having their own materials were forced to discharge
concurrently and composition of the gradient layer formed on the
substrate 8 was adjusted by controlling power applied to each of
the targets. Specifically, the power of the SrRuO.sub.3 target 10
was maximized at the start of formation of the mixture layer and
then reduced gradually to zero at the end of formation of the
mixture layer. The power of the Pt target 9, adversely, was set to
zero at the start of formation of the mixture layer and then
increased gradually to a maximal value at the end of formation of
the mixture layer.
For comparison, a lower electrode was manufactured in a
configuration in which Ta and Pt were set to 50 nm and 850 nm
respectively from the substrate 8, and also a thickness was made
totally equal.
Then, on the lower electrode formed in such a way, a PZT film was
formed with a thickness of about 3 to 5 .mu.m by an aerosol
deposition method using the device shown in FIG. 1.
Conditions for film formation by the aerosol deposition method at
this time are as follows.
Material used: PZT-LQ from SAKAI CHEMICAL INDUSTRY CO., LTD.
Initial particle size: 0.2 to 0.5 .mu.m
Temperature at film formation: room temperature
Air flow into the aerosol formation chamber: 4 cc/min
Differential pressure between both chambers: about 67 kPa
Next, this PZT film was ground to a film thickness of 3.+-.0.1
.mu.m by a grinder and uniformity of in-plane distribution was
improved, providing a piezoelectric film.
Next, the substrate 8 having up to this piezoelectric film formed
thereon along with fine particles for raw material was put in a
container of ziruconia, and all even with the container were baked
at 900.degree. C. in an electric furnace. Putting in the fine
particles for raw material together is because Pb is prevented from
dropping out due to baking and further a portion from which Pb
drops is compensated for.
A rate of raising and lowering temperature was set to 2.degree.
C./rain and baking was held at 900.degree. C. for one hour.
After baking, an upper electrode was provided by forming Ta of 50
nm and Pt of 150 nm on the PZT film by a magnetron sputter
method.
The piezoelectric element formed in such a way was measured for a
dielectric constant and an equivalent piezoelectric constant (d31)
as electric characteristics. A variable used for computation of the
piezoelectric constant was measured with applying a voltage to a
sample which was formed by cutting off the piezoelectric element
above in form of cantilever. Further, Young's moduli of both the
substrate and the piezoelectric film were derived from measurement
by a nanoindenter. Moreover, a diffusion sate was estimated by
examining each component of the electrode, the piezoelectric film
and the substrate by using SIMS.
Each of the results was shown in Table 1.
The comparative sample was not able to be measured for electric
characteristics, because the lower electrode diffused into the
surface of the piezoelectric film due to baking after formation of
the piezoelectric film, and accordingly leakage between the lower
and upper electrode occurred due to film formation of the upper
electrode. Further, also in analysis of the depth direction by
SIMS, it was observed that Ta diffused up to the surface of the
piezoelectric film and further Pb diffused into the Si wafer of the
substrate.
On the contrary, in the electrode configuration of the present
invention, high values of the dielectric constant and d31 for
electric characteristics were exhibited. Further, from analysis of
the diffusion state in the depth direction by SIMS (Secondary Ion
Mass Spectrometry), it was found that components of the electrode
did not diffuse into PZT, and only Pb of components of PZT diffused
into the electrode, but it did not reach the substrate 8.
TABLE-US-00001 TABLE 1 Estimation PZT/Pt/Pt--SrRuO.sub.3 graded
items film/SrRuO.sub.3/substrate PZT/Pt/Ta/substrate Dielectric
2100 not measurable constant d31 99 pC/N not measurable Diffusion
Pb diffusion partway to Pb diffusion to the state the electrode is
substrate is confirmed confirmed Pb diffusion to the Ta diffusion
to PZT substrate is not observed is confirmed Diffusion of the
electrode layer into PZT is not observed
Next, to confirm adherence between each of the layers, tape peel
test was carried out on the lower electrodes of two type
configurations described below in which a film thickness of the
mixture layer was made different. One of the two type
configurations was that on a Si wafer for a substrate 8,
SrRuO.sub.3 as an electroconductive oxide layer, next a mixture
layer having a composition ratio of SrRuO.sub.3 and Pt which has a
gradient in the film thickness direction, and next Pt as an
electroconductive metal layer were stacked in this order. The other
configuration was that on a Si wafer for a substrate 8, SrRuO.sub.3
as an electroconductive oxide layer, next a mixture layer having a
composition ratio of SrRuO.sub.3 and Ir which has a gradient in the
film thickness direction, and next Ir as an electroconductive metal
layer were stacked in this order. These lower electrodes having
different thicknesses of the mixture layers were tested for
adherence using a tape. This was carried out using a method by
which, after the lower electrode was formed on the Si wafer for the
substrate 8, notches in form of 25 grids with a size of 5
mm.times.5 mm were cut in the relevant lower electrode in a dicing
process, and a mending tape was bonded to the lower electrode
having the notches cut therein, and then the number of pieces which
peeled was estimated. FIG. 3 is a schematic depiction illustrating
a section of the lower electrode cut in form of grid. As shown in
FIG. 3, the relevant lower electrode 12 was cut up to a substrate
11 to cut completely.
A film thickness of SrRuO.sub.3 was set to 100 nm, film thicknesses
of Pt layer and Ir layer were set to 100 nm and a film thickness of
a mixture layer having a gradient was changed from 0 to 10 .mu.m,
and thus estimation was carried out. In addition, the thickness of
the mixture layer was adjusted by controlling duration of sputter
discharge time. The result of the tape peel test on the electrode
is shown in Table 2.
TABLE-US-00002 TABLE 2 Thickness of the mixture layer 0 5 10 100 1
2 10 nm nm nm nm .mu.m .mu.m .mu.m Tape test Pt--SrRuO.sub.3 25 12
0 0 0 5 7 (the number Ir--SrRuO.sub.3 25 8 0 0 0 2 3 of pieces
which peeled/ total 25)
Even in either case, adherence between each of the layers was
insufficient when the thickness of the mixture layer was not
greater than 5 nm, and particularly, and when the mixture layer was
absent, the electroconductive oxide layer peeled completely from
the electroconductive metal layer. Strong adherence without peel
was able to be provided when the thickness of the mixture layer was
not smaller than 10 nm and not larger than 1 .mu.m.
Example 2
An ink jet head was formed by forming a piezoelectric element on a
vibrating plate including a Si substrate, next forming a flow path
in a FIB process and finally bonding an orifice plate having a
discharge hole. Formation processes will be described with
reference to FIGS. 4A, 4B, 4C, 4D, 5A, 5B, 5C and 5D.
First, similar to the example 1, SrRuO.sub.3 of 300 nm constituting
an electroconductive oxide layer, a mixture layer of 300 nm having
a composition ratio of SrRuO.sub.3 and Pt which has a gradient in
the film thickness direction, and Pt of 300 nm constituting an
electroconductive metal layer were formed in this order by a
magnetron sputter method on a vibrating plate (substrate) 41
including quartz glass as a lower electrode 42. Next, by the
aerosol deposition method shown in FIG. 1, a PZT film constituting
a piezoelectric film 43 having a thickness of about 5 .mu.m was
formed entirely on the substrate 41 (on the electroconductive oxide
layer). Next, baking was carried out in atmospheric air at
900.degree. C. for one hour. A raising and lowering rate of
temperature was set to 2.degree. C./rain. Subsequently, Ti of 40
nm, Pt of 160 nm for an upper electrode 44 were formed (FIG.
4A).
Next, positive resist was applied to etch the upper electrode 44,
forming a resist pattern 45 (FIG. 4B). Next, by RIE (Reactive Ion
Etching), Pt and Ti exposed on the upper electrode 44 were etched
(FIG. 4C). Next, the resist for the upper electrode was removed and
resist 46 for PZT was patterned to surround the upper electrode 44
(FIG. 4D). In this situation, a PZT film was etched using fluoric
nitric acid (FIG. 5A), subsequently the resist was removed (FIG.
5B). Next, a flow path 47 was formed in a FIB process (FIG. 50).
After cleaning, the Si substrate with a discharge hole as an
orifice plate 48 was bonded, and finally, the substrate 41 was cut
to provide an ink jet head (FIG. 5D).
In this example, SrRuO.sub.3 was used as an electroconductive oxide
and lead zirconate titanate (PZT) was used as a piezoelectric film,
but not limited to these.
Further, in this example, the PZT film was patterned as described
above, but when the PZT film was formed by the aerosol deposition
method, a patterning method may be used by which a mask having an
opening was inserted between a nozzle and the substrate. Moreover,
also for formation of the PZT film, any of a sputter method, a
sol-gel method, a CVD method and the like may be used. The
piezoelectric element of the present invention may be applied to an
electronic device using a heretofore known piezoelectric element.
The electronic device may include a wide range of devices, for
example, a piezoelectric actuator, a pressure sensor or an ink jet
device.
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
This application claims the benefit of Japanese Patent Application
Nos. 2006-101451, filed Apr. 3, 2006, and 2007-052325, filed Mar.
2, 2007, which are hereby incorporated by reference herein in their
entirety.
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